The present invention relates to a thin film magnetic head suitable for high-density magnetic recording.
In recent years, magnetic recording with higher density and higher performance has been developed remarkably. Especially in the field of a magnetic disc device for a large-sized computer, capacity has been increased as a result of a significant improvement in recording density. In magnetic disc devices, a thin-film magnetic head having a smaller inductance, a larger high-frequency permeability and a narrower track width as compared with conventional ferrite heads has been put into practical use. As described in JP-A-55-87323 (published on Jul. 2, 1980, and corresponding to U.S. application Ser. No. 972,102 filed on Dec. 21, 1978, now U.S. Pat. No. 4,219,855), thin film magnetic heads are conventionally fabricated by using Ni-Fe (permalloy) alloys each having a saturation magnetic flux density of 1 T.
FIG. 1 is a sectional view of a principal part of a thin film magnetic head formed by using a Ni-Fe alloy. With reference to FIG. 1, an Al.sub.2 O.sub.3 film 12 is formed on an insulating substrate 1 comprising Al.sub.2 O.sub.3 -TiC ceramics, Al.sub.2 O.sub.3 -TiO.sub.2 ceramics, SiC, Zn ferrite, Ni-Zn ferrite, Mn-Zn ferrite or the like by sputtering. A lower magnetic core member 2' is formed by sputtering a Ni-Fe alloy. The layer thickness is 1.5 .mu.m. A non-magnetic gap 3 is formed by sputtering Al.sub.2 O.sub.3. As an insulating layer 5 of a coil conductor 4, heat-resisting polyimide resin or a resist material is used. The coil conductor 4 is formed by sputtering Cu. In the same way as the lower magnetic core member 2', an upper magnetic core member 10 is formed by sputtering a Ni-Fe alloy. The film thickness is chosen to be 2.0 .mu.m. The representative composition of the Ni-Fe alloy is 81 wt % Ni-19 wt % Fe, for which the magnetostriction becomes zero. Further, a protective layer 7 having a thickness substantially equivalent to 20 .mu.m is formed on the above described magnetic core member 10. Patterning of the lower magnetic core member 2', the non-magnetic gap 3, the coil conductor 4 and the upper magnetic core member 10 is formed by using the ion milling method.
In order to improve the recording density, the coercive force of the medium must be raised. In order to cope with this, the thickness of the magnetic core member must be made large so that a large number of magnetic lines of force may emerge from the tip of the head core. If the thickness of the magnetic core member is made large, however, a resulting decrease in the reproduction resolution especially poses a problem, although it is a matter of course that the recording resolution is also decreased. It is said that a conventional head having a magnetic core comprising a Ni-Fe alloy having a saturation magnetic flux density 1 T cannot sufficiently cope with future problems of both a higher coercive force of the medium and a lower reproduction resolution caused by an increase in recording density and a magnetic material having a high saturation magnetic flux density must be used for a magnetic layer constituting a magnetic core member.
In recent years, an amorphous sputter layer has been developed as a magnetic layer having a high saturation magnetic flux density and a high performance (high permeability). Among the rest, an amorphous alloy comprising Zr and Hf as amorphous state establishing elements is especially excellent in corrosion resistance and wear resistance and has excellent properties for use as a magnetic layer for a magnetic head. More specifically, the amorphous alloy is represented by the composition formula MaTbAc, where M denotes at least one of Co, Fe, Ni and the like each having a magnetic moment and A denotes at least one of Zr, Hf and the like each having a large atomic radius. T denotes a transition metal other than M and A. Especially, a Co-Ta-Zr amorphous alloy, a Co-Ta-Hf amorphous alloy and a Co-Ta-Hf-Pd amorphous alloy as described in JP-A-58-98824 (published on Jun. 11, 1983) and JP-A-60-21504 (published on Feb. 2, 1985) are regarded as promising for use as the magnetic layer for a thin film magnetic head because a saturation magnetic flux density of 1.3 T is obtained at a magnetostriction of zero in each of them. As for a crystal alloy layer, a multilayer structure comprising an Fe-C alloy and a Ni-Fe alloy and a multilayer structure comprising an Fe-Si-Ru alloy and a Ni-Fe alloy have been developed as a high-performance magnetic layer having a high saturation magnetic flux density as described in JP-A-59-130408 (published on Jul. 27, 1984).
As another material of a magnetic layer having a high saturation magnetic flux density, a 45 wt % Ni-55 wt % Fe alloy is known. Since the 45 wt % Ni-55 wt % Fe alloy has a large positive magnetostriction, however, a variation in the reproduction output of a thin film head using it is large, resulting in a problem. Further, since the permeability is as small as 1,300 to 1,400, the reproduction output is also small as compared with a thin film magnetic head using 81 wt % Ni-19 wt % Fe (permalloy), resulting in another problem.
In JP-A-60-10410 (published on Jan. 19, 1985, and corresponding to U.S. application Ser. No. 508,207 filed on Jun. 27, 1983, now U.S. Pat. No. 4,589,042), this problem is coped with by using a 45 wt % Ni-55 wt % Fe alloy having a large saturation magnetic flux density only in the tip region of the magnetic core and a 81 wt % Ni-19 wt % Fe alloy having a high permeability and a small negative magnetostriction in other portions substantially defining the reproduction output.
As a material having a high saturation magnetic flux density, a Co-Zr amorphous alloy layer is known. The Co-Zr amorphous alloy has a large anisotropic magnetic field immediately after sputtering and has a permeability as small as 700 to 800. A thin film magnetic head using this alloy thus has a problem that the reproduction output is small.
In JP-A-58-68211 (published on Apr. 23, 1983), this problem is coped with by combining a Co-Fe-B amorphous layer having a high permeability and a Co-Zr amorphous layer having a high saturation magnetic flux density.
In view of the fact that the magnetic flux converges in the vicinity of the gap of the magnetic core, the above described JP-A-58-68211 copes with the above described problem by forming a magnetic core with two kinds of magnetic layers and making the saturation magnetic flux density of the magnetic layer in the vicinity of the gap larger.